The present invention relates to an image processor, and more particularly, to an image processor which draws a high quality oblique line.
Generally, a conventional image processor has difficulty displaying an oblique straight line. The line is typically displayed in a step-like shape. This is called aliasing. To smoothly display the oblique straight line, a conventional image processor performs an anti-alias program. The conventional image processor processes image data outside a frame buffer based on the anti-alias program, and then the image processor stores the image data in the frame buffer. Such a conventional image processor is disclosed in, for example, Fujio Yamaguchi et al. "Practical computer graphics", Nikkankogyo Shinbun Co., Feb. 28, 1987, the first impression of the first edition, pp. 118-125.
The conventional image processor, however, has a problem because the anti-alias process is performed by software. Therefore, it is difficult to accelerate the anti-alias process.
In addition, the conventional image processor has another problem because the anti-alias process uses color data expressed in an RGB color space. Human visual characteristics are sensitive to a change of brightness rather than a change of chromaticity. Therefore, if a change of color brightness is sharp, even if color density or hue do not change, the change stands out and is sensed. In this circumstance, while it is preferable to continuously change the brightness for performing high quality anti-alias processing, the color data expressed in the RGB color space cannot make continuous changes of the brightness. This is because it is impossible, in the RGB color space, to dissolve the color data to brightness and chromaticity. This is the reason why sufficient quality cannot be obtained if the color data is used while being expressed in the RGB color space.